Field
Devices, apparatuses, methods, and articles of manufacture consistent with the present disclosure relate to an image sensor, and more particularly, to an image sensor using a global counter, an analog-to-digital converter, and an analog-to-digital converting method.
Description of the Related Art
In recent years, the use of mobile devices such as a smart phone, a tablet PC, a digital camera, an MP3 player, an e-book, etc. is exploding. Most mobile devices include one or more image sensors to capture an image. Image sensors may include a charge coupled device (hereinafter, referred to as CCD) image sensor and a CMOS image sensor.
Noise of the CCD image sensor is less than that of the CMOS image sensor. Also, a picture quality of the CCD image sensor is better than that of the CMOS image sensor. However, a driving method of the CMOS image sensor is simple, and the CMOS image sensor is implemented by various scanning methods. Also, since a signal processing circuit is integrated in a single chip, it is possible to fabricate a small-sized product. Since a CMOS process technique is compatibly used, a production cost is lowered. Since power consumption of the CMOS image sensor is very low, it is easy to apply the CMOS image sensor to a mobile device.
The CMOS image sensor includes an analog-to-digital converter that converts an image signal sensed as an analog signal into a digital signal. A pixel array of an image sensor has a plurality of pixels arranged in a two-dimensional matrix form, and each pixel outputs an image signal from a light energy. Each pixel integrates photo-charges corresponding to the amount of light incident through a photo diode and outputs an analog current type of pixel signal according to the integrated photo-charges. The pixel signals are converted into digital signals through the analog-to-digital converter (hereinafter, referred to as ADC).
An ADC circuit is provided for every column line of the pixel array to convert an analog signal from the pixel array of the image sensor into a digital signal. In this case, the number of ADC circuits is controlled by the number of column lines of the pixel array, and as the number increases significant burden in terms of power consumption and area arises. In addition, a large current peak occurs according to ADC operations simultaneously performed at respective columns, and the current peak thus generated acts as a noise of the image sensor.